SPI microgels applied to Pickering stabilization of O/W emulsions by ultrasound and high-pressure homogenization: rheology and spray drying

Soybean Protein Isolate (SPI) is a by-product from soybean oil industries with good nutritional and functional properties. Denaturation of hydrated SPI can change its properties, allowing the formation of gel-like particles, which can be used to stabilize emulsions without addition of surfactants. SPI microgel particles were produced by denaturation of hydrated SPI, followed by high pressure homogenization or sonication, with different NaCl or NaF contents, aiming the formation of small particles capable to stabilize O/W emulsions and acting as wall material for microencapsulation of soybean oil by spray drying. The presence of NaF in the suspensions decreased the charge intensity of SPI microgels, leading to formation of significantly bigger SPI microgel particles. Based on Creaming Index (CI), all the emulsions were stable for, at least, 21 days at room temperature. The presence of salt affected minimally the droplet size of the emulsions, though there has been an increase in flocculation. All the emulsions presented shear-thinning behavior and a strong shear rate dependence when salt was present in the system. The microspheres produced by spray drying of the emulsions were spherical and showed few aggregate formation. In addition, they presented high values of oil retention (> 80 wt%) and acceptable values of moisture content (< 4 wt%). SPI microgel particles produced by high-pressure homogenization or sonication may be used to stabilize emulsions with low oil contents. These emulsions can be further spray dried to microencapsulate lipophilic compounds using SPI microgels as wall material.